Monkey Study Suggests Long-Term ADHD Drug Use Appears Safe

Between 5 to 7 percent of elementary school children are diagnosed with ADHD, according to researchers from the Wake Forest Baptist Medical Center who undertook the new study.

Many of these children are treated with psychostimulant drugs, and while doctors and scientists know a lot about how these drugs work and their effectiveness, little is known about their long-term effects, the researchers note.

The research team, headed by Linda Porrino, Ph.D., professor and chair of the Department of Physiology and Pharmacology, and fellow professor Michael A. Nader, Ph.D., conducted a study with monkeys to determine what the long-lasting effects may be.

“We know that the drugs used to treat ADHD are very effective, but there have always been concerns about the long-lasting effects of these drugs,” she said. “We didn’t know whether taking these drugs over a long period could harm brain development in some way or possibly lead to abuse of drugs later in adolescence.”

The researchers studied 16 monkeys, whose ages were equivalent to 6- to 10-year-old humans. Eight animals were in the control group that did not receive any drug treatment. The other eight were treated with a therapeutic-level dose of an extended-release form of Ritalin or methylphenidate (MPH) for over a year, which is equivalent to about four years in children.

Imaging of the monkeys’ brains, both before and after the study, was conducted on both groups to measure brain chemistry and structure. The researchers also looked at developmental milestones to address concerns that ADHD drugs adversely affect physical growth.

Once the drug treatment and imaging studies were concluded, the monkeys were given the opportunity to self-administer cocaine over several months. Nader measured their propensity to acquire the drug and looked at what amounts to provide an index of vulnerability to substance abuse in adolescence.

The researchers found that there were no differences between the two groups — monkeys treated with Ritalin during adolescence were not more vulnerable to later drug use than the control animals.

“After one year of drug therapy, we found no long-lasting effects on the neurochemistry of the brain, no changes in the structure of the developing brain. There was also no increase in the susceptibility for drug abuse later in adolescence,” Porrino said.

“We were very careful to give the drugs in the same doses that would be given to children. That’s one of the great advantages of our study is that it’s directly translatable to children.

The research was conducted simultaneously with a “sister study” at John Hopkins with slightly older animals and different drugs and their findings were similar, she added.

“We feel very confident of the results because we have replicated each other’s studies within the same time frame and gotten similar results,” she said. “We think that’s pretty powerful and reassuring.”

This study is published online in the journal Neuropsychopharmacology.

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